Since a new season of COCI (Croatian Open Competition in Informatics) started last saturday, here is the first in a series of COCI appreciation posts (I will post one after each COCI round, so six in total!). For my coaching, I went through all COCI contests since 2006 to gather tasks and selected some of my favorite ones.

Notes

• I skipped a lot of the really hard tasks because they weren't useful for my students. I kept a list of these tasks, if someone wants it, they can PM me. Also, I only considered COCI, not COI. This current season is not being considered.
• There are many great tasks outside of the 48 shown (throughout the series), so it's worth it to go through other tasks as well. I have selected just my favorite ones.
• These tasks are maybe not always the most innovative, I have selected the tasks that are most useful for coaching and learning new ideas, so for people who already know the idea, the difficulty might be much lower. Still, there are some really interesting tasks.
• You can do these tasks either individually or as a virtual contest. There are a lot of them, so I guess I wouldn't recommend less than 3h.
• The notes are meant for coaches to know if they can use that task for a lecture that they are preparing. They can also serve as hints for competitors (but sometimes they just give out the solution). Both the tags and the notes should be considered spoilers.
• The given difficulty ranges might be completely wrong as I might be out of touch with the easier grades, they are just given as a loose guide.